1. Field of the Invention
The invention relates to a process for producing hydrodynamic bearings for supporting and guiding rotary machine shafts, particularly shafts operating at high rotational speeds; the invention relates more particularly to the construction of bearings comprising thin foils conditioning the formation of a fluid film supporting the shaft when this latter is set in rotation. The invention extends to hydrodynamic bearings produced by using the process, as well as secondary assemblies designated further on by the term "self-contained cartridges", which, in accordance with the invention, are previously manufactured for producing the bearings.
By "hydrodynamic bearings" is meant not only bearings in which the support is obtained by a gas film but also those where it is obtained by a liquid film.
2. Description of the Prior Art
It is known that, in rotary high-speed machines, fluid film support or suspension bearings are advantageously used which avoid any contact between solid surfaces. Two essential types of bearings of this kind are known at present: hydrostatic bearings which have the defect of requiring a pressure source and hydrodynamic bearings in which the supporting fluid film is produced by rotation of the shaft and which present then the advantage of being self-contained. In this latter type of bearing, the foil bearings are the most widely known and are used in the majority of cases; they comprise a plurality of thin curved foils which are fixed inside the bore of a bearing shell, so as to partially overlap and form an internal floating surface forming a succession of "support corners" which generate the creation of the fluid film between the foils and the shaft when this latter reaches a sufficient rotational speed. Reference may be made for example to French Pat. No. 1 454 024 filed on Aug. 18th, 1965 for further details concerning these hydrodynamic foil bearings. In the known bearings of this type, the curved foils are generally made from thin metal sheet and are fixed individually inside the bearing shell by means of hollow structures such as grooves, furrows or calibrated holes which are machined in the shell so as to open into the internal surface thereof; each foil is provided with a preformed end having a shape adapted for fitting into the hollow structure which corresponds thereto and each of said foils is individually fixed in said hollow structure of the bearing shell by means of fixing members such as keys, pins, screws etc . . . .
This forming process presents serious drawbacks. Firstly, machining of the bearing shells and, to a lesser extent, the manufacture of the members for fixing each foil are relatively costly operations which very appreciably increase the cost of the bearings obtained. Moreover, this type of construction requires the use of bearing shells of great thickness so that the above-mentioned hollow structures may be machined therein and the members for fixing each foil housed therein.
Furthermore, the individual fitting of the foils into the bearing shell is an extremely delicate operation because of the high geometric precision required; such an operation, carried out either during a maintenance operation on the rotary machine concerned or during the assembly of this latter, requires qualified staff who must be sent on the site with special tools and who often meet with unfavorable working conditions, making these operations for adjusting the foils long and difficult to carry out. This drawback is particularly serious in the case of maintenance operations which become long and expensive when, at the end of their normal operating time, a number of bearings must be equipped with new thin foil.
In addition, the individual handling of each thin foil for assembly often causes deformation thereof or impairs their surface condition, which may be prejudicial to the correct formation of the supporting fluid film and so to correct operation of the bearing.
The present invention proposes a solution palliating the above-mentioned defects of hydrodynamic foil bearings.